1. Field of the Invention
The field of the invention concerns a connecting plug for a high-voltage cable.
2. Description of Related Art
In the field of medical diagnostic X-ray equipments, special connecting devices are provided for electrically connecting an appliance, such as an X-ray source for example, to a generator of high-voltage power.
Standards exist to specify the electrical and structural constraints that must be fulfilled by these connecting devices.
In particular, the XR-7 standard, established by the NEMA (National Electrical Manufacturers Association) for power-supply voltages of between 10 kV (kilovolts) and 200 kV, specifies constraints of shape and geometrical dimensions that must be fulfilled by the different components of connecting devices.
Compliance with these standards allows interoperability to be provided between the generators of high-voltage power and the different medical appliances requiring a high-voltage power supply.
A connecting device typically has two separable parts, namely a male part (known also as a plug), which constitutes one end of the high-voltage cable, and a female part (also called a receptacle or a socket), which is fixed in a permanent manner to the casing of the generator or of the equipment to be supplied, and designed to receive the male part. In order to withstand high voltages, the receptacle and the plug are made from rigid and electrically insulating materials. The receptacle and the plug have shapes and dimensions that are imposed by the standards.
The plug and the receptacle must be insulated from each other in order to avoid the formation of electrical arcs between the receptacle, the plug and the metallic envelopes of the cable forming an earth.
At the present time, the electrical insulation between the plug and the receptacle is generally achieved by means of an insulating liquid. The space that exists between the plug and the receptacle is filled with a liquid insulator, such as oil or grease for example.
In practice, the use of an insulating liquid raises certain problems.
In particular, the introduction of oil or of grease is a difficult operation since it requires a total absence of air bubbles or of polluting conducting particles between the plug and the receptacle.
In addition, there is always a risk that the operator who makes the connection will forget to inject the liquid insulator or will do so imperfectly.
Moreover, the presence of an insulating liquid imposes a substantially vertical orientation of the connecting device during fitting and removal.
In operation, the connecting device can be at a relatively high temperature. The differences in thermal expansion between the different components of the device, including the liquid insulator, give rise to a potential risk of breaking the seal of the device, which can lead to leakage of the liquid insulator and, as a consequence, deterioration of the electrical insulation.
Finally, the sealing problems arise even more in the case of radiological appliances whose X-ray source, powered at high voltage, is in motion. This is the case, for example, of computed tomography (CAT scan) appliances in which the X-ray source is rotated around the patient. The movement of the source favours the leakage of liquid insulator, in the event of a poorly sealed connection.
Document FR 2 879 031 A1 proposes replacement of the liquid insulator by an insulating interface in the form of a sleeve made of a flexible insulating material, such as a silicone elastomer for example. The interface includes segments that have elongated rings separated by air chambers.
This type of interface is particularly suitable for connecting devices of small size, but is not suitable for connecting devices of large dimension, of the type that are specified by the XR-7 standard.
In fact, with connecting devices that have a large longitudinal dimension, the sleeve of flexible material has a tendency to slide along the plug and to deform during insertion of the plug into the receptacle. The consequence is to render difficult the insertion of the plug into the receptacle and to result in incorrect positioning of the sleeve in the connecting device.